1. Field of the Invention
The present invention relates to the protection of birds that migrate at night and, more particularly, to an infrasound hazard warning device for that purpose.
2. The Related Art
A serious problem for night-migrating bird populations is collisions with buildings and communication towers, and this problem is expected to increase dramatically over the next two years. Television stations are expected to build as many as 100,000 tall towers ( greater than 200 ft) in the next decade to meet the mandate of the Federal Communication Commission to digitize all television stations by the year 2003. The cumulative impact of all towers and buildings on the migrating bird populations in North America pose a significant threat to their viability.
As far as the inventor is aware, there is no known method or device that effectively warns birds of buildings and tower locations and their potential hazard at night. The Federal Aviation Administration requires pilot warning lights on all towers over 20 ft. tall, but, unfortunately, the birds are attracted to these lights. Further, it has been found that red pulsating lights attract birds more than do white strobes.
A principle object of the invention is to warn the approximately 350 species of night-migrating songbirds in North America of obstacles in their path, particularly tall buildings and communication towers with pilot warning lights, so that the large numbers of fatalities which occur each year can be avoided.
As will appear, a key feature of the invention is the use of infrasound to mimic natural obstacles or lightning strikes that birds avoid naturally, due to the workings of their innate navigational system.
Previous work by the inventor on infrasound and the avian navigational map indicates that birds use infrasonic map cues radiated by steep-sided topographic features to navigate over great distances (hundreds to thousands of miles). Infrasonic signals travel thousands of miles in the atmosphere with little attenuation, and birds have extremely sensitive low-frequency hearing. Pigeons can detect sounds with frequencies as low as 0.05 Hz. Birds are able to navigate through mountain valleys and passes at night, or in other conditions of limited visibility, because they can detect the underlying topography from the infrasound radiated thereby.
The present invention is based on the inventive appreciation that if artificial obstacles or attached devices are made to radiate infrasound at the same frequency as natural topographic features, then night-migrating birds will avoid them in the same way as they would avoid colliding with, e.g., a hillside. An alternative embodiment is based on experiments that show that birds in flight react to and move away from artificially-generated thunder sounds. In accordance with this alternative embodiment, a method and device are provided for repeatedly radiating the sound of thunder at infrasonic frequencies. The device is attached to artificial obstacles to be avoided, e.g., buildings and communication towers, especially in conjunction with white strobe lights, so as to cause birds to avoid in-flight collisions with these artificial obstacles.
In accordance with a first aspect of the invention, there is provided a hazard warning device for night-migrating birds for warning the birds of the presence of a fixed structure against which the birds could collide during night-migration, the device comprising a speaker device affixed to the structure; and a recorder means connected to the speaker device for, when activated, supplying to the speaker device, for continuous broadcast thereby, an infrasonic signal which naturally causes the birds to avoid the structure.
According to one embodiment of this aspect of the invention, the recorder means comprises a recorder for supplying an infrasonic signal to the speaker device which causes the birds to avoid the structure based on the workings of the innate navigational system of the birds. Preferably, the signal has a frequency at least close to that of a natural topographic feature.
According to a further embodiment of this aspect of the invention, the recorder means comprises a recorder for supplying to the speaker device an infrasonic signal representative of a natural occurring weather threat to the birds. Preferably, the recorder supplies a signal which reproduces or mimics the sound of thunder and/or reproduces or mimics the sound of a lightning strike.
Advantageously, the speaker device comprises a sub-subwoofer and resonant cavity capable of broadcasting at frequencies of 0.1 to 50 Hz.
In accordance with a second aspect of the invention, there is provided a method for warning night-migrating birds of the presence of an obstacle against which the birds could collide during night migration, the method comprising: affixing a speaker device to the obstacle; and supplying to speaker device, for broadcast thereby, an infrasonic signal which naturally causes the birds to avoid the obstacle.
According to one embodiment of this aspect of the invention, the signal causes the birds to avoid the obstacle based on the workings of the innate navigational system of the birds. Preferably, the signal has a frequency at least close to that of a natural topographic feature.
According to a further embodiment of this aspect of the invention, the signal comprises an infrasonic signal representative of a natural occurring weather threat to the birds. Preferably, the signal reproduces or mimics the sound of thunder and/or reproduces or mimics the sound of a lightning strike. Advantageously, the signal is broadcast in conjunction with the strobing of white lights.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.